U.S. patent number 6,854,985 [Application Number 09/465,056] was granted by the patent office on 2005-02-15 for elastomeric interconnection device and methods for making same.
This patent grant is currently assigned to Paricon Technologies Corporation. Invention is credited to Roger E. Weiss.
United States Patent |
6,854,985 |
Weiss |
February 15, 2005 |
**Please see images for:
( Certificate of Correction ) ** |
Elastomeric interconnection device and methods for making same
Abstract
An elastomeric device for interconnecting two or more electrical
components, comprising, an elastomeric matrix having one or more
outer surfaces; one or more electrically conductive pathways
through the matrix; and one or more electrically conductive contact
pads, wherein at least a portion of one or more of the pads is
flush with or extends outward from one or more of the outer
surfaces of the matrix, and wherein at least a portion of the pad
is in at least intimate contact with one or more of the pathways;
and methods for making same.
Inventors: |
Weiss; Roger E. (Foxboro,
MA) |
Assignee: |
Paricon Technologies
Corporation (Fall River, MA)
|
Family
ID: |
34118147 |
Appl.
No.: |
09/465,056 |
Filed: |
December 16, 1999 |
Current U.S.
Class: |
439/91; 439/591;
439/66; 439/74; 439/86 |
Current CPC
Class: |
H01R
13/2414 (20130101); H01R 4/26 (20130101); H01R
43/007 (20130101) |
Current International
Class: |
H01R
13/24 (20060101); H01R 13/22 (20060101); H01R
43/00 (20060101); H01R 4/26 (20060101); H01R
4/00 (20060101); H01R 004/58 () |
Field of
Search: |
;439/66,74,86,91,591 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Nguyen; Truc
Attorney, Agent or Firm: Dingman, Esq.; Brian M. Mirick,
O'Connell, DeMallie & Lougee, LLP
Parent Case Text
This application claims benefit of provisional 60/112,535 filed
Dec. 16, 1998.
Claims
What is claimed is:
1. An elastomeric device for electrically interconnecting two or
more components, comprising: an elastomeric matrix having one or
more outer surfaces; a plurality of electrically conductive
pathways through said matrix, the pathways each comprising a
plurality of particles; and a plurality of electrically conductive
contact pads integral with said matrix, said pads each in
electrical contact with a plurality of conductive pathways, wherein
at least a portion of one or more of said is flush with or extends
outward from an outer surface of said matrix.
2. The device of claim 1, further comprising one or more means for
providing flow space into which at least a portion of said matrix
may flow under compression.
3. The device of claim 2, wherein said means for providing flow
space comprises one or more compressible microspheres imbedded in
said matrix.
4. The device of claim 2, wherein said means for providing flow
space comprises spaces formed between a plurality of raised surface
asperities on one or more of said outer surfaces of said
matrix.
5. The device of claim 2, wherein said means for providing flow
space comprises one or more gas particles located in said
matrix.
6. The device of claim 5, wherein said pathways comprise one or
more conducting particles and wherein said gas particles are of a
size which is about 20% or less than the size of said conducting
particles.
7. The device of claim 2, wherein said means for providing flow
space comprises one or more spaces formed between two or more of
said pads which extend outward from said surface of said
matrix.
8. The device of claim 2, further comprising one or more asperities
on one or more of said outer surfaces, wherein said means for
providing flow space comprises one or more spaces formed between
two or more of said asperities.
9. The device of claim 2, wherein one or more of said pathways
comprises a plurality of electrically conductive particles, wherein
one or more of said particles extends outward from one or more of
said outer surfaces, and wherein said means for providing flow
space comprises one or more spaces formed between two or more of
said particles extending outward from said one or more of said
surfaces.
10. The device of claim 1, wherein said pathways are anisotropic
and comprise up to about 25% magnetic particles by volume of said
elastomeric matrix.
11. The device of claim 10, wherein a plurality of said magnetic
particles are aligned to form one or more arrays of electrically
isolated columns having at least one end, wherein one or more of
said pads is in contact with an end of one or more of said columns
of particles.
12. The device of claim 1, wherein one or more of said pathways
comprises a plurality of particles aligned to form a column having
at least one end, wherein one or more of said pads is in contact
with at least one of said ends of one or more of said columns of
particles.
13. The device of claim 1, wherein one or more of said pads
comprises one or more layers of metal in at least intimate contact
with one or more of said outer surfaces of said matrix.
14. The device of claim 13, wherein said pads together form an
array of electrically conductive pads across one or more of said
outer surfaces of said matrix.
15. The device of claim 14, wherein at least one of said components
is a circuit board comprising an array of electrical contact
points, (lands), and wherein said array of pads corresponds to said
array of contact points on said board.
16. The device of claim 14, wherein at least one of said components
is a heat sink, and wherein said matrix is isotropic to conduct
heat from said circuit board to said heat sink.
17. The device of claim 14, wherein at least one of said components
is a ball grid array comprising an array of solder balls, and
wherein said array of pads corresponds to said array of solder
balls.
18. The device of claim 1, wherein one or more of said pathways
comprises a plurality of electrically conductive particles aligned
in a column having at least one end particle coated with a metal,
and wherein said portion of said pad, that is in at least intimate
contact with one or more of said pathways, is in contact with said
coated end particle and is coated with one or more metals that is
compatible with said metal coating on said end particle.
19. The device of claim 1, wherein said matrix comprises one or
more elastomers which retains about 90% or more of its modulus of
compression over a temperature range of between about -50.degree.
C. to 200.degree. C.
20. The device of claim 1, wherein one or more of said pads has at
least one outer surface, wherein at least a portion of said outer
surface comprises one or more electrically conductive coatings.
21. The device of claim 20, wherein one or more of said coatings
comprises one or more metallic layers.
22. The device of claim 1, wherein one or more of said pads has at
least one outer surface comprising one or more asperities.
23. The device of claim 1, wherein one or more of said pathways
comprise a plurality of conducting particles aligned in one or more
columns having at least one end particle, and wherein one or more
of said pads form a bond with said matrix and with one or more of
said end particles.
24. The device of claim 1, wherein said outer surfaces of said
matrix comprise a first surface adapted to face one of said
components and a second surface adapted to face a second of said
components, wherein one or more of said pathways extends from at
least proximate to said first surface to at least proximate said
second surface and wherein one or more of said pads are located on
said first and second surfaces.
25. The device of claim 1, further comprising one or more support
films.
26. The device of claim 25, wherein at least one of said support
films is a carrier sheet.
27. The device of claim 25, wherein at least one of said support
films is removable.
28. The device of claim 25, wherein one or more of said components
comprises registration holes, and wherein at least one of said
films comprises one or more registration holes in said film which
correspond to said registration holes of said component.
29. The device of claim 25, wherein one or more of said components
comprises registration holes, and wherein one or more of said films
comprises one or more precision pins which correspond to one or
more of said registration holes of said components.
30. The device of claim 25, wherein at least one of said films
comprises one or more mounting holes in said film which are at
least partially filled with said elastomeric matrix.
31. The device of claim 25, wherein at least one of said films
comprises one or more contact holes adapted to receive therein at
least one or more of said pads.
32. The device of claim 31, wherein at least one of said films is
removable, which, if removed, will leave behind spaces between two
or more of said pads into which at least a portion of said matrix
may flow when compressed.
33. The device of claim 25, wherein at least one of said films
comprises one or more contact holes adapted to receive therein at
least one or more of said pads, and wherein at least one or more of
said pads has an outer surface which protrudes from said contact
holes.
34. The device of claim 25, wherein at least one of said films
comprises one or more contact holes adapted to receive therein at
least one or more of said pads, and wherein at least one or more of
said pads has at least an outer surface which is exposed and coated
with one or more metals.
35. The device of claim 1, wherein a plurality of said pads are
mounted to said matrix as an applique.
36. The device of claim 35, wherein said applique comprises a
support layer which holds one or more of said pads in one or more
predetermined locations in said support layer.
37. The device of claim 36, wherein one or more of said pathways
comprise a plurality of conducting particles aligned in one or more
columns having at least one end particle proximate one or more of
said outer surfaces of said matrix, wherein said predetermined
locations correspond to one or more of said end particles.
38. The device of claim 36, wherein said support layer comprises
two opposing sides, wherein one or more of said pads which is held
in said support layer comprises two opposing ends portions which
are larger in diameter than a middle portion, wherein said holes of
said support layer have a diameter which is smaller than the
diameters of said opposing ends, and wherein said larger opposing
end portions of one or more of said pads extend outward from said
opposing sides of said support layer and said middle portion of
said pad is captured in said hole.
39. The device of claim 38, wherein said middle portion of said pad
has a length and said pad is capable of floating up and down in
said hole to the extent of said length of said middle portion.
40. The device of claim 38, wherein said pads are brass.
41. The device of claim 38, wherein said pads are molded plastic
and comprise one or more conductive layers.
42. The device of claim 41, wherein said conductive layers comprise
a layer of copper and one or more subsequent layers of nickel and
solder.
43. The device of claim 41, wherein said conductive layers comprise
a first layer of copper, a second layer of nickel and one or more
subsequent layers of gold.
44. The device of claim 38, wherein said pads have one or more
surfaces and comprise one or more asperities in one or more of said
pad surfaces.
45. The device of claim 38, wherein said pads comprise conductive
plastic.
46. A method for making an elastomeric device for electrically
interconnecting two or more components, comprises the steps of,
embedding a plurality of conductive, magnetic particles in an
elastomer which retains 90% of its modulus of compression over a
temperature range of between about -50.degree. C. to 200.degree. C.
by mixing said particles in said elastomer before said elastomer
sets and applying a magnetic force to said particles so that said
particles align themselves in electrically isolated columns as the
elastomer sets to form an elastomeric matrix having one or more
outer surfaces and comprising one or more electrically conductive
pathways through said matrix; providing one or more electrically
conductive contact pads; and fixing one or more of said
electrically conductive contact pads to said matrix, so that at
least a portion of one or more of said pads is flush with or
extends outward from one or more of said outer surfaces of said
matrix and, so that at least a portion of said pad is in at least
intimate contact with one or more of said pathways.
47. The method of claim 46, further comprising the step of creating
one or more means for providing flow space into which at least a
portion of said matrix may flow under compression.
48. The method of claim 47, wherein said step of creating one or
more means for providing flow space comprises embedding one or more
compressible microspheres in said elastomer as its sets to form
said matrix.
49. The method of claim 47, wherein said step of creating one or
more means for providing flow space comprises forming a plurality
of raised surface asperities in one or more of said outer surfaces
of said matrix as said elastomer sets.
50. The method of claim 47, wherein said step of creating one or
more means for providing flow space comprises the step of trapping
one or more gas particles in said matrix as said elastomer
sets.
51. The method of claim 46, wherein said pathways are anisotropic
and comprise up to about 25% magnetic particles by volume of said
elastomeric matrix.
52. The method of claim 51, wherein a plurality of said columns of
magnetic particles has at least one end particle proximate one or
more of said outer surface of said matrix, and wherein one or more
of said pads is in intimate contact with an end particle of one or
more of said columns of particles.
53. The method of claim 51, wherein said pathways comprise at least
about 3% magnetic particles by volume of said elastomeric
matrix.
54. The method of claim 46, wherein one or more of said pathways
has at least one end particle, and wherein one or more of said pads
is in intimate contact with at least one of s aid end particles of
one or more of said columns of particles.
55. The method of claim 46, wherein one or more of said pads
comprises one or more layers of metal in at least intimate contact
with one or more of said outer surfaces of said matrix and one or
more of said pathways.
56. The method of claim 46, wherein said pads are a known number
and comprise two opposing end portions having a diameter and a
middle portion having a diameter smaller than said diameter of said
end portions, and wherein said step of providing one or more
electrically conductive contact pads comprises the steps of,
providing one or more non-conductive, pliant support sheets
comprising a plurality of holes, having a diameter smaller than
said diameter of said end portion of said pads, through said sheet
corresponding to said number of pads; and pushing one of said
opposing ends portions of each of said pads through one of said
holes so that said pad is captured in said sheet.
57. A device package, wherein one or more chips and one or more
components are electrically interconnected, comprising, one or more
layers of elastomeric material between said chip and said
component, wherein at least one of said layers provide electrical
contact between said chip and said component, and wherein said
layer which provides electrical contact comprises, an elastomeric
matrix having one or more outer surfaces; one or more electrically
conductive pathways through said matrix; and one or more
electrically conductive contact pads, wherein at least a portion of
said pad is in at least intimate contact with one or more of said
pathways.
58. A device package, wherein one or more chips and one or more
heat sinks are interconnected so that heat may be transferred from
said chip to said heat sink, comprising, a can having a first and
second opposing surface, wherein said first opposing surface is
adjacent to said heat sink; a top layer of elastomeric material
provided between said chip and said second opposing surface of said
can, wherein said top layer provides thermal contact between said
chip and said can; a bottom layer of conducting elastomeric
material between said chip and a lead frame, wherein said bottom
layer provides electrical contact between said chip and said lead
frame.
59. The device package of claim 58, wherein said bottom layer
comprises elastomeric conducting polymer interconnect.
Description
FIELD OF THE INVENTION
This invention relates to improved conductive elastomer
interconnection devices and methods for making them.
BACKGROUND OF THE INVENTION
As electronic systems get smaller, faster and lower cost, the
classic methods of separable interconnection need to be replaced
with new technologies. One such technology is based on anisotropic
conducting polymer materials. Anisotropic Conducting Elastomers
(ACE) are elastomers which conduct in one direction but are
insulators in the other direction. One such example is
ECPI--(Elastomeric Conducting Polymer Interconnect) a material
developed by Lucent Technologies--Bell Laboratories. This material
is formed by magnetically aligning fine magnetic particles in
sheets of uncured silicone such that the particles form arrays of
electrically isolated columns. These columns are frozen in place as
the silicone cures. When a layer of ECPI is compressed between two
electrical conductors the particles in the compressed column come
into contact with each other and the conductors, forming an
electrically conductive path. Conductivity of the column remains
over a compression range which is a function of the material
design. This range, often referred to as the material's dynamic
range, provides compensation for the lack of coplanarity of the
conductors. This is often referred to as "coplanarity
compensation".
In a typical application of ACE the interconnect formed replaces
the soldered interconnect to allow a separable interconnection.
Separable interconnection is generally required for testing the
device, conditioning the device (burn-in) and for final application
in the OEM product. One such example is in a Land Grid Array (LGA)
where an array of pads on a device needs to be connected to a
matching array on a board. A second example is when a Ball Grid
Array (BGA), consisting of a device with an array of solder balls,
is to be separably connected to a matching array on the board. In
both of these examples, a layer of ACE material placed between the
device and the board can, when properly used, provide a reliable
connection.
Further, when using ECPI as an interconnection medium between BGA
devices, because the solder balls come in direct contact with the
conducting particles on the outer surface of the ECPI, the
spherical shape of the solder balls tend to bow the columns of
particles outward from the contact center rather than compressing
the columns in a straight line. The bowing may cause poor
interconnection and shorting between adjacent pads.
Moreover, the behavior of the elastomeric material is critical to
the success of the interconnect's performance. Typically highly
filled elastomeric material exhibit poor elastic properties, and
when formed into discrete button-like contacts, tended to move like
putty, taking a severe set. These materials exhibit little residual
spring force. These factors impact on the reliability of the
contact, and virtually preclude multiple device insertions with
different devices. Because these highly filled materials have poor
elastic properties, an external spring member is required to create
a contact force. However, the elastomer button-like contacts flow
continuously under the force. The conventional solution is to limit
the flow with a stop. The net effect is a very low contact force.
In addition, elastomers in sheet form may have excellent elastic
properties but tend to behave like incompressible fluids. This
behavior demands that the connector system design provide for a
place for the material to move.
Another problem arises because, unlike conventional pin-in-socket
contacts which provide for a metal to metal wiping action as the
pin mates with the socket, elastomeric contacts tend to provide no
wipe. This wiping action breaks through surface contaminants and
corrosion products, such as oxides and sulfides. Moreover, improper
selection of contact materials, such as solder against a gold
plated particle, can result in the gold dissolving in the solder
and forming a brittle alloy which will break and form a type of
insulating layer referred to as fretting corrosion.
The above described limitations to the capability of conventional
elastomeric conducting materials may, to a varying extent, be
applied to both anisotropically conducting elastomeric materials
that have magnetically aligned particles, and isotropically
conducting materials such as those that are heavily filled with
conducting metal. These limitations also apply to some extent to
anisotropic elastomeric materials that utilize other means than the
magnetic alignment of particles to provide electrical and/or
thermal connection.
SUMMARY OF THE INVENTION
The device and methods of the invention provide unique improvements
to both anisotropic and isotropic conductive elastomers, and more
specifically to ECPI, which enhance performance and reliability and
to broaden their range of applications. These improvements include,
but are not limited to, improved polymer materials, unique surface
geometries and improved connectors housing the polymers. Unlike
previous ECPI, the devices and methods of the invention utilize
metal contact pads which are compatible with the underlying
conductive particles of the ECPI; and the elastomeric material of
the device facilitates penetration of unwanted contaminants using
the nodular structure of the particles at the surface of the
elastomer or by asperities formed on the pads.
It is therefore a primary object of this invention to provide a
device, for anisotropically or isotropically interconnecting two or
more components, which enhances the quality and reliability of the
interconnection.
It is a further object of this invention to provide a device, for
interconnecting two or more components, which is capable of
repeated use for testing, conditioning and final application of the
components.
It is a further object of this invention to provide a device, for
interconnecting two or more components, having an outer surface
which is durable and readily cleaned.
It is a further object of this invention to provide a device, for
interconnecting two or more components, capable of being
selectively coated with metals or solders which are compatible with
opposing component surfaces to prevent fretting corrosion, to
improve the interconnection and to improve the versatility of the
device.
It is a further object of this invention to provide a device, for
interconnecting two or more components, such as a Ball Grid Array
and a board, which prevents the conductive columns of particles of
the device from bowing when compressed between the components.
It is a further object of this invention to provide a device, for
interconnecting two or more components, which provides flow space
into which the elastomer materials in the device may flow under
compression.
It is a further object of this invention to provide a device, for
interconnecting two or more components, which provides additional
surface features, including one or more contact pads, which protect
the underlying conductive particles and improve conductivity
between the device and the opposing components.
It is a further object of this invention to provide a device, for
interconnecting two or more components, comprising one or more
contact pads on which one or more asperities are formed to
penetrate any oxide layer formed on an opposing component and to
improve the interconnection.
It is a further object of this invention to provide a device, for
interconnecting two or more components, comprising one or more
contact pads, fixed to the matrix of the device, which prevent the
underlying conducting particles at the outer surface of the matrix
from dislodging.
It is a further object of this invention to provide a device, for
interconnecting two or more components, comprising one or more
contact pads on which one or more layers of metal are formed to
improve the interconnection.
It is a further object of this invention to provide a device, for
interconnecting two or more components, comprising one or more
floating contact pads capable of being separably applied to an
underlying conductive matrix.
A preferred embodiment of the elastomeric device of the invention
for electrically interconnecting two or more components, comprises:
an elastomeric matrix having one or more outer surfaces; one or
more electrically conductive pathways through the matrix; and one
or more electrically conductive contact pads, wherein at least a
portion of one or more of the pads is flush with or extends outward
from one or more of the outer surfaces of the matrix and, wherein
at least a portion of the pad is in at least intimate contact with
one or more of the pathways. The matrix preferably comprises one or
more elastomers which retains about 90% or more of its modulus of
compression over a temperature range of between about -50.degree.
C. to 200.degree. C. The device may further comprise one or more
means for providing flow space into which at least a portion of the
matrix may flow under compression; wherein the means for providing
flow space may comprise one or more of the following: one or more
microspheres imbedded in the matrix; one or more spaces formed
between two or more of the pads which extend outward from the
surface of the matrix; one or more spaces formed between a
plurality of raised surface asperities on one or more of the outer
surfaces of the matrix; and one or more gas particles (a bubble of
controlled size) located in the matrix. In the latter instance, the
pathways may also comprise one or more conducting particles and
wherein the gas particles are of a size which is about 20% or less
than the size of the conducting particles.
The device may also further comprise one or more asperities on one
or more of the outer surfaces, wherein the means for providing flow
space comprises one or more spaces formed between two or more of
the asperities; and/or wherein one or more of the pathways
comprises a plurality of electrically conductive particles, wherein
one or more of the particles extends outward from one or more of
the outer surfaces, and wherein the means for providing flow space
comprises one or more spaces formed between two or more of the
particles extending outward from the one or more of the
surfaces.
The elastomeric matrices may be isotropic or anisotropic, where, in
the latter instance, the matrices preferably comprise between about
5 to 25% magnetic particles by volume of the elastomeric matrix;
wherein a plurality of the magnetic particles are preferably
aligned to form one or more arrays of electrically isolated columns
having at least one end, wherein one or more of the pads is in
contact with an end of one or more of the columns of particles. In
a device wherein one or more of the pathways comprises a plurality
of particles aligned to form a column having at least one end and
wherein one or more of the pathways is anisotropic, one or more of
the pads is preferably in contact with at least one of the ends of
one or more of the columns of particles.
One or more of the pads may comprise one or more layers of a
conductive material, preferably metal, in at least intimate contact
with one or more of the outer surfaces of the matrix; and may
together form an array of electrically conductive pads across one
or more of the outer surfaces of the matrix. One or more of the
pads may further comprise one or more outer surfaces comprising one
or more asperities. The pads may be applied to the matrix by
sputtering, vapor deposition, plating, bonding or a combination of
these techniques.
In applications wherein at least one of the components is a circuit
board comprising an array of electrical contact points, (lands),
the array of pads preferably corresponds to the array of contact
points on the board. In applications wherein at least one of the
components is a heat sink, the pathways are isotropic to conduct
heat away from the circuit board to the heat sink. In applications
wherein at least one of the components is a ball grid array
comprising an array of solder balls, the array of pads preferably
corresponds to the array of solder balls.
As noted one or more of the pathways of conductive particles
comprises a plurality of electrically conductive particles aligned
in a column. These particles may have at least one end particle
coated with a metal, wherein the portion of the pad, that is in at
least intimate contact with one or more of the pathways, is
preferably in contact with the coated end particle and is coated
with one or more metals that is compatible with the metal coating
on the end particle; wherein one or more of the pads preferably
forms a bond with the matrix and with one or more of the end
particles.
The outer surfaces of the matrix typically comprises a first
surface adapted to face one of the components and a second surface
adapted to face a second of the components, wherein one or more of
the pathways extends from at least proximate to the first surface
to at least proximate the second surface and wherein one or more of
the pads are located on the first and second surfaces.
The device of the invention may further comprise one or more
support films; wherein at least one of the support films is
preferably a carrier sheet; wherein at least one of the support
films is preferably removable; wherein one or more of the
components may comprise registration holes, and wherein at least
one of the films comprises one or more registration holes in the
film which correspond to the registration holes of the component
and through which one or more alignment members, such as a
precision pin, may be passed. In instances wherein one or more of
the components comprises registration holes, one or more of the
films may comprise one or more precision pins which correspond to
one or more of the registration holes of the components. At least
one of the films may comprise one or more mounting holes in the
film which are at least partially filled with the elastomeric
matrix; and/or at least one of the films comprises one or more
contact holes may be adapted to receive therein at least one or
more of the pads, wherein at least one or more of the pads may have
an outer surface which protrudes from the contact holes. In
instances wherein at least one of the films is removable, the
removable film, if removed, will preferably leave behind spaces
between two or more of the pads into which at least a portion of
the matrix may flow when compressed.
The pads of the device may be mounted to the matrix as an applique,
wherein one embodiment of the applique comprises a support layer
which holds one or more of the pads in one or more predetermined
locations in the support layer; and wherein one or more of the
pathways may comprise a plurality of conducting particles aligned
in one or more columns having at least one end particle proximate
one or more of the outer surfaces of the matrix, wherein the
predetermined locations correspond to one or more of the end
particles. The support layer may comprise two opposing sides,
wherein one or more of the pads which is held in the support layer
comprises two opposing ends portions which are larger in diameter
than a middle portion, wherein the holes of the support layer have
a diameter which is smaller than the diameters of the opposing
ends, and wherein the larger opposing end portions of one or more
of the pads extend outward from the opposing sides of the support
layer and the middle portion of the pad is captured in the hole.
The middle portion of the pad preferably has a length, wherein the
pad is capable of floating up and down in the hole to the extent of
the length of the middle portion. The floating pads are preferably
brass. Alternatively, the floating pads may be molded plastic
comprising one or more conductive layers, wherein the conductive
layers comprise a layer of copper and one or more subsequent layers
of nickel and solder or gold. The floating pads may likewise
comprise one or more asperities in one or more of the pad
surfaces.
The preferred method of the invention, for making an elastomeric
device for electrically interconnecting two or more components,
comprises the steps of: embedding a plurality of conductive,
magnetic particles in an elastomer which retains 90% of its modulus
of compression over a temperature range of between about
-50.degree. C. to 200.degree. C. by mixing the particles in the
elastomer before the elastomer sets and applying a magnetic force
to the particles so that the particles align themselves in
electrically isolated columns as the elastomer sets to form an
elastomeric matrix having one or more outer surfaces and comprising
one or more electrically conductive pathways through the matrix;
providing one or more electrically conductive contact pads; and
fixing one or more of the electrically conductive contact pads to
the matrix, so that at least a portion of one or more of the pads
is flush with or extends outward from one or more of the outer
surfaces of the matrix and, so that at least a portion of the pad
is in at least intimate contact with one or more of the pathways.
The method may further comprise the step of creating one or more
means for providing flow space into which at least a portion of the
matrix may flow under compression, wherein the step of creating one
or more means for providing flow space comprises embedding one or
more microspheres in the elastomer as its sets to form the matrix;
forming a plurality of raised surface asperities in one or more of
the outer surfaces of the matrix as the elastomer sets; and/or
trapping one or more gas particles in the matrix as the elastomer
sets. One or more of the pads comprises one or more layers of metal
in at least intimate contact with one or more of the outer surfaces
of the matrix and one or more of the pathways.
The conductive pathways used in the method of the invention may be
anisotropic and may comprise up to about 25% magnetic particles by
volume of the elastomeric matrix, wherein a plurality of the
columns of magnetic particles has at least one end particle
proximate one or more of the outer surface of the matrix, and
wherein one or more of the pads is in intimate contact with an end
particle of one or more of the columns of particles. The conductive
pathways preferably comprise at least about 3% magnetic particles
by volume of the elastomeric material. The elastomeric matrix may
alternatively be isotropic and comprise at least one end particle
wherein one or more of the pads is in intimate contact with at
least one of the particles in the matrix.
If an applique of pads is used in the method, the pads may be of a
known number and may comprise two opposing end portions having a
diameter and a middle portion having a diameter smaller than the
diameter of the end portions, and wherein the step of providing one
or more electrically conductive contact pads comprises the steps
of, providing one or more non-conductive, pliant support sheets
comprising a plurality of holes, having a diameter smaller than the
diameter of the end portion of the pads, through the sheet
corresponding to the number of pads; and pushing one of the
opposing ends portions of each of the pads through one of the holes
so that the pad is captured in the sheet.
The device of the invention may be incorporated into a device
package, wherein one or more chips and one or more components are
electrically interconnected, comprising: one or more layers of
elastomeric material between the chip and the component, wherein at
least one of the layers provide electrical contact between the chip
and the component, and wherein the layer which provides electrical
contact comprises, an elastomeric matrix having one or more outer
surfaces; one or more electrically conductive pathways through the
matrix; and one or more electrically conductive contact pads,
wherein at least a portion of the pad is in at least intimate
contact with one or more of the pathways.
Another preferred embodiment of the device of the invention
incorporated into a device package, wherein one or more chips and
one or more heat sinks are interconnected so that heat may be
transferred from the chip to the heat sink, comprises: a can having
a first and second opposing surface, wherein the first opposing
surface is adjacent to the heat sink; a top layer of elastomeric
material provided between the chip and the second opposing surface
of the can, wherein the top layer provides thermal contact between
the chip and the can; a bottom layer of conducting elastomeric
material between the chip and a lead frame, wherein the bottom
layers provides electrical contact between the chip and the lead
frame; wherein the bottom layer preferably comprises elastomeric
conducting polymer interconnect.
BRIEF DESCRIPTION OF THE DRAWINGS
Other objects, features and advantages will occur to those skilled
in the art from the following description of the preferred
embodiments and the accompanying drawings in which:
FIG. 1A is a partial cross-sectional view of a prior art
elastomeric conductor using magnetically aligned particles;
FIG. 1B is a partial cross-sectional view of the prior art
conductor of FIG. 1A plasma etched to expose the outer surface of
the conductive particles embedded therein;
FIG. 2 is a partial perspective cross-sectional view of the device
of the invention;
FIG. 3 is a partial cross-sectional view of another preferred
embodiment of the device of the invention;
FIG. 4 is a partial cross-sectional view of another preferred
embodiment of the device of the invention;
FIG. 5 is a partial cross-sectional view of another preferred
embodiment of the device of the invention;
FIG. 6A is a partial cross-sectional view of another preferred
embodiment of the device of the invention;
FIG. 6B is a partial cross-sectional view of the device of FIG. 6A
with the carrier partially removed;
FIG. 6C is a partial cross-sectional view of the device of FIG. 6A
with the carrier completely removed;
FIG. 6D is a partial cross-sectional view of the device of FIG. 6A
with the carrier completely removed and the outer surface of the
pads are plated;
FIG. 7 is a partial cross-sectional view of another preferred
embodiment of the device of the invention;
FIG. 8 is a partial cross-sectional view of another preferred
embodiment of the device of the invention;
FIG. 9 is a partial cross-sectional view of another preferred
embodiment of the device of the invention;
FIG. 10 is a partial cross-sectional view of another preferred
embodiment of the device of the invention;
FIG. 11 is a partial cross-sectional view of another preferred
embodiment of the device of the invention;
FIG. 12 is a partial cross-sectional view of another preferred
embodiment of the device of the invention;
FIG. 13 is a partial cross-sectional view of another preferred
embodiment of the device of the invention;
FIG. 14 is a partial cross-sectional view of another preferred
embodiment of the device of the invention comprising an applique of
floating pads;
FIG. 15 is a cross-section of a floating pad shown in FIG. 11;
FIG. 16 is partial cross-sectional view of another preferred
embodiment of an applique of floating pads of the invention;
and
FIG. 17 is a cross-sectional view of the device of the invention in
use.
DETAILED DESCRIPTION OF THE PREFERRED METHOD
The elastomeric device of the invention, for electrically
interconnecting two or more components, generally includes the
following basic elements: an elastomeric matrix having one or more
outer surfaces; one or more electrically conductive pathways
through the matrix; and one or more electrically conductive contact
pads, wherein at least a portion of one or more of the pads is
flush with or extends outward from one or more of the outer
surfaces of the matrix and, wherein at least a portion of the pad
is in at least intimate contact with one or more of the pathways.
As described below, each of these basic elements may be modified to
suit a particular application and/or to optimize certain features
of these elements. Generally, the device may include pads which are
integral with the matrix and/or pads which are separable, as in an
array of pads which are mounted to the matrix as an applique.
Integrated Surface Pads
FIG. 1A is a cross-section of the typical elastomeric conductor of
the prior art using magnetically aligned conducting particles. As
shown in FIG. 1A, a thin layer of polymer material remains on the
surface after manufacturing which must be penetrated by the
particles as the conductor is squeezed between two components. FIG.
1B shows the thin polymer material etched away in a manner taught
by U.S. Pat. No. 4,820,376, "Fabrication of CPI Layers". When
exposed, the particles are quite fragile and the material must be
handled very carefully to prevent the particles from
dislodging.
The preferred embodiment of the device of the invention is shown
and generally referred to in FIG. 2 as device 10. Device 10
comprises an array of integral conducting pads 12 formed on the
surfaces 24 and 26 of matrix 18 and in intimate contact with the
surfaces and one or more conducting particles such as particles 14
and 16, each located at the end of a column of magnetically aligned
particles such as column 20. Device 10 may also include other
surface features such as routing path 22. The array of pads 12 can
be formed by sputtering, vapor deposition, plating, bonding or a
combination of these methods that are well understood by those
skilled in the metal surface formation industries. The pads may be
formed directly on the surface of the elastomer or as an applique
on a separate sheet and subsequently bonded to the elastomer as
described later in this disclosure.
The resulting pad(s) form a bond between the silicone of matrix 18
and the end particles of the columns of conducting particles. The
pads protect the end particles and keeps them from dislodging from
the matrix. The pads also serve as extended electrical contact area
improves the overall efficiency of an electrical connection. This
geometry is particularly well suited for interconnecting BGA
devices. Each solder ball on the BGA may now contact a matching pad
on matrix 18, which, in turn, is in contact with an end particle of
several conducting particle columns. This design allows the device
to be compressed between the BGA and a circuit board without
causing the columns of conducting particles to bow as frequently
happens when the typically round solder balls of the BGA are
compressed directly against the ends of the columns of conducting
particles of the devices shown in FIGS. 1A and 1B.
Although device 10 comprises pads on both surfaces of matrix 18, it
is envisioned that pads and other surface features may be formed on
one or both surfaces and may facilitate a multiplicity of
electrical paths throughout matrix 18 and across the surface of
matrix 18 to augment the routing provided by the device and a board
or other component.
The pad structure provides a readily cleaned protective layer,
which greatly increases the usable life of the material.
Furthermore, a secondary cleaning operation of the plasma etched
material with integral pads will remove the surface particles from
unwanted areas while leaving the particles only in the pad area.
This will minimize the opportunity for unwanted electrical
contact.
The thickness of pads 12, and thus the height of pads 12 which
extends outward from the outer surfaces of matrix 18, forms spaces,
e.g. space 28, between adjacent pads into which the polymer of
matrix 18 may flow or bulge as the polymer material is compressed
between two opposing components. Spaces, such as space 28, allow
the elastomeric material to be used in applications where no local
expansion space is provided, such as with designs using solder mask
around the lands, which causes the lands to be coplanar or recessed
relative to the surface of the solder mask.
The outer surface of the pad may be structured so as to optimize
the interconnection with the opposing component. The pad's outer
surface may be finished with solder, gold or any material that is
an optimum match of the opposing member. Different finishes may be
provided on opposing surfaces of the pads to facilitate the
interconnection between normally inappropriate materials, such as
solder to gold.
Asperities may be desired and formed on the surface of the pads to
puncture any oxide layers on the surface of the opposing components
and to provide a more reliable interconnection. The asperities may
be formed on the pad surface by various means, as shown in FIGS.
3-5. As shown by device 30 in FIG. 3, if the pad 36 is thin
relative to the surface particles 34, asperities 32 are formed by
virtue of the sharp edges of the underlying particles embedded in
matrix 38 which protrude from the outer surface of the pad. In
instances where the thickness of the pad prevents the particles
from protruding, a secondary plating step may be used to form
dendrites 42 on the outer surface of the pad 46 of device 40 (FIG.
4). The dendrites may be formed using the plating method taught in
U.S. Pat. No. 5,185,073 or by forming diamond shards on the surface
as taught in U.S. Pat. No. 5,835,359. Alternatively, chemical or
mechanical methods, such as etching and sand blasting, may be
employed to roughen the base metal of the surface of pad 52 of
device 50 while having little effect on the surrounding elastomer.
A subsequent thin plating 54 of a hard metal such as nickel
followed by a thin surface plate will provide an ideal surface
which is well populated with asperities (FIG. 5).
Typically, the device testing arena requires conducting elastomers
which have a very robust and easily cleaned surface to optimize the
maximum cycle life of the elastomers. In the present invention, the
pad, by covering the end particles, provides such as surface as a
durable conductor surface. Moreover, the surface of the elastomer
matrix, in between the pads, may be coated with a debris resistant
film such as a flexible solder mask which is also durable and
readily cleaned.
In the normal construction of an elastomeric conductive sheet, a
carrier film such as a 0.005 inch thick layer of Mylar is used to
carry the elastomeric film through the manufacturing process. This
carrier sheet is normally removed from the elastomer at the end of
the assembly. In yet another embodiment of the device of the
invention, shown and generally referred to in FIGS. 6A-6D as device
60 comprising matrix 62, the carrier sheet 64 is modified with an
additional thin support film 66. Support film 66 has holes formed
in it corresponding to the pattern of the contacts. For example,
the film may comprise a 0.002 inch thick film of Kapton with 0.025
inch holes formed on 0.050 inch centers. Other features such as
registration and mounting holes may also be formed in the support
sheet.
When the elastomeric matrix is formed it will fill the holes in
support film 66. When carrier sheet 64 is removed from support film
66 (FIG. 6B), a structure comprising elastomeric matrix 62 and
support film 66 remains. The support film seals the surface of the
elastomeric matrix and particles embedded therein and provides
additional dimensional stability to the structure. The exposed pads
67 are then etched and plated, e.g. plate 68, as described earlier,
with aspirates as needed. The resulting structure (FIG. 6D)
provides a stable, sealed surface which can be readily cleaned.
This structure facilitates repeated use as needed for test sockets
and burn-in sockets.
In yet another preferred embodiment, shown and generally referred
to in FIG. 7 as device 70, device 70 comprises matrix 72, carrier
sheet 78 and two additional support films 74 and 76. Device 80
(FIG. 8) comprises matrix 82, support film 84 and modified carrier
sheet 86. When sheet 78 and film 76 or modified sheet 86 are
removed from their respective devices small spaces, e.g. spaces 90,
are left between the surface of the pads and the surrounding area,
as shown in FIG. 9. The spaces serve two purposes: they allow the
device to access lands 102 on the opposing component 100 which are
surrounded by solder mask 104 and are depressed relative to the
solder mask (FIG. 10) and it also provides a space 106 for the
elastomer to flow to during compression. The protruding pads may or
may not be metalized as described earlier based on the
application.
Registration of the array of pads to the lands can be achieved by
the addition of other features to the Kapton sheet. In one such
preferred embodiment shown and generally referred to in FIG. 11 as
device 110, four precision registration holes are placed in the
Kapton sheet 112 outside matrix 114 and array of pads, e.g.
registration holes 116 and 118. Fewer or more registration holes
may be employed depending on the application. These holes match
four equivalent holes in the opposing component such as a printed
wiring board. Alignment of the pads on the matrix to the lands on
the board is facilitated with precision pins pressed through the
holes in the Kapton into the matching holes in the printed wiring
board. These precision pins can be molded into the device alignment
frame which provides alignment of the device to the board in a
single molded piece part. Any elastomeric material covering the
registration holes in the Kapton should be easily penetrated by the
pins. Alternatively, the matrix may be die cut and predetermined
section removed from the carrier sheet. Other features, such as
registration slots, can be added to the Kapton sheet to align it
with the connector housing, support frames or other alignment and
support devices commonly used.
In yet another preferred embodiment shown in FIG. 12, the array of
pads 124 are formed by well understood methods on a separate
carrier sheet 122. In this embodiment, a Kapton sheet 123 may also
be attached to carrier sheet 122 which is in intimate contact with
the pads and contains registration holes 116 and 118. The pads are
copper and are coated with conductive adhesive 125. The carrier
sheet assembly is laminated to a sheet of ECPI 121 bonding the pads
to the ECPI sheet. The carrier sheet is peeled away leaving the
pads and Kapton sheet attached to the ECPI.
In another preferred embodiment shown in FIG. 13, carrier sheet 133
with Kapton 133 and copper pads 134 is built without the conductive
adhesive. Sheet 133 is coated with the uncured ECPI formulation and
run through the ECPI manufacturing process. The resulting sheet of
ECPI 131 is intimately bonded to the copper pads and Kapton carrier
sheet. The carrier sheet is peeled away leaving the pads and Kapton
sheet attached to the ECPI.
As previously noted, although the device 110 has pads on only one
surface, the device may be modified to provide pads on both
surfaces, with the support film on one or both sides of the
elastomeric matrix. The structure described above can be combined
in several ways to address the interconnection needs of a specific
application.
Separable Surface Pads
There are several applications where it is advantageous to have the
pad layer as a separate structure or applique which may be mounted
on the outer surface of the matrix of the device. The applique
would be aligned relative to the device and an opposing component,
e.g. a circuit board, but the matrix of the device would not
require orientation relative to the pad layer. FIG. 14 shows such a
structure. With this structure the pad would serve as the interface
between matrix 148 and the component contact. The matrix would
provide the needed compliance to allow for interconnection between
the components.
One preferred embodiment of the applique, generally shown and
referred to in FIG. 14 as applique 142 of device 140, would
comprise a nonconductive sheet 144, such as Kapton, which has holes
146 formed on the same grid as the contact array. These holes would
be populated by small floating pads 150. Depending on the
application, these pads typically would have a diameter comparable
to the land or solder ball diameter, and a height of between about
0.010 to 0.020 inch. They would have a reduced diameter middle
portion 152 (FIG. 15) or "waist" and two opposing ends portions 154
and 156 which are larger in diameter than the middle portion,
wherein the holes 146 of the nonconductive sheet or support layer
have a diameter which is smaller than the diameters of the opposing
ends, which would allow the pads to be captured in the hole in the
Kapton. The compliance of the Kapton would allow for one of the
ends of the pads to be actively pushed through the hole without
pushing the opposing end through the hole as well. The pad floats
in the hole by virtue of the reduced diameter middle portion and is
retained in the hole by virtue of the larger end portions. The pad
could move up and down the length of the waist while being held in
place laterally.
The floating pads may be machined from metal such as brass using a
screw machine tool, and barrel plated with gold or solder.
Alternatively, the floating pad may be molded from plastic and
plated to create the conductive path. The plating process starts
with an electroless copper plate and is followed with nickel and
solder or gold as needed. These plating techniques are well known
to those skilled in the art of plating. The metal coatings could
alternatively be applied by overmolding techniques where the molds
are plated first with a metal, such as silver, before filling the
molds with the plastic material. Asperities 158 (FIG. 15) may be
formed on the pads by using a mold insert having a roughened inside
surface and may be coated with plating 151.
In another preferred embodiment of the applique, shown and
generally referred to as applique 160, sheet 162 and pads 164 are
molded out of plastic, with or without molded asperities 166, and
plated with conductive plate 168. The shape of the pads may be
optimized to match the opposing contact. The applique of this
embodiment may be made by inserting a Kapton carrier with holes on
the component grid into a molding press where plateable conducting
contacts are then molded into each of the holes. The geometry of
the pads and any asperities desired would be defined by the
geometry and inside surface of the molding press. The resulting
contacts pads would be electrolessly plated with conductive
materials that would not plate on the Kapton, providing the needed
array of plated contact pads.
Alternatively, an integral molded lead frame may be used to
mechanically orient the plurality of pads so that they were held on
the contact grid, thus eliminating the need for the carrier sheet.
The pads would be preferentially plated with the appropriate metal
system to address the needs of the interconnection. The lead frame
would, in its final state, not be plated, leaving it
non-conductive. This can be facilitated by several different
methods.
One such method utilizes a double molding process, wherein the lead
frame and contact pads are molded from different plastics. The pads
are be formed from a plateable plastic and the lead frame is formed
from a non-plateable plastic.
In another method, the entire surface of the contact pad and lead
frame would be plated with a thin flash of copper, providing a
conductive path for electroplating. A non-plateable photo resist
would be coated over the entire part, and processed to be removed
from the contacts but remain on the lead frame. The assembly would
then be electroplated with nickel, followed by gold, solder or any
other suitable material, as needed. The photoresist on the lead
frame is removed, and the copper flash etched from the frame,
eliminating conductive paths. The etch will not attack the solder
or gold finish on the contacts.
In yet another method, the contact pads are preferentially
metalized by masking the lead frame and applying metal by
sputtering or other form of vapor deposition.
The above described methods may be combined in numerous ways to
achieve the desired geometry. One such combination would comprise
the step of molding a contact pad array with lead frame attached.
This entire assembly is then plated with the techniques described
above. The array of contacts pads would be gang inserted into a
Kapton sheet with matching holes. As the array of pads is inserted,
the lead frame is removed and discarded.
Bulk Properties of Elastomer
Magnetically aligned systems, such as ACEs, use very little metal,
and the material tends to take on the elastic behavior of the base
elastomer. However, as noted above, the behavior of the elastomeric
material is critical to the success of the device's performance.
Previously used materials, such as highly filled materials,
typically exhibit little residual spring force which reduces the
reliability of the contact and virtually precludes multiple device
insertions with different devices. In the present invention, these
drawbacks are overcome by using a recently developed "perfectly"
elastic base elastomers which exhibit nearly perfect elasticity
over a broad temperature range. Specifically, NuSil CF1-6755
(available from NuSil Technology, Carpinteria, Calif.) has been
identified as having close to ideal behavior. In a preferred
embodiment, the matrix is formed from a blend of from 5% to 25% by
volume of magnetically aligned particles in a base of NuSil
CF1-6755 or its equivalent (by equivalent is meant an elastomeric
material that retains at least 90% of its modulus of compression
over a temperature range of -50.degree. C. to 200.degree. C.). This
combination will not take a set over a wide temperature range.
When these "perfectly" elastic materials are used to interconnect
components to other components, such as boards, external clamping
springs such as those required by other types of sockets, are no
longer required. Closure of the socket to a fixed displacement of
the ACE material will establish a spring force which will remain
fixed over the life of the product.
As noted, elastomers tend to behave like incompressible fluids. A
distribution of space must be provided for the elastomer to flow or
bulge into as the material is compressed. Several methods may be
employed to form the needed flow space. For example, as noted
above, the surface structure can be modified by the addition of
conducting pads as described above. A volume of space is created by
the thickness of the pads. These pads would be on the same grid as
the contacts of the device and board. In addition, or
alternatively, microspheres of compressible material, such as air
filled particles, may be introduced into the matrix of
elastomer.
In yet another alternative method, foamed elastomer materials may
be utilized which combine the elastic properties of the NuSil
silicone (available from NuSil Technology, Carpinteria, Calif.)
described above with the ability to create highly controlled size
and distribution gas particles throughout the elastomer matrix.
Such a material, for example, is NuSil Silicone Foam CF3-2350. In a
general sense, the pore size or diameter of entrained gas particle
should be less than 20% the size of the conducting particle. This
material will be a perfectly elastic medium which is
compressible.
In yet another method for creating the elastomer sheet, the
conventional practice is to use a flat carrier web. The elastomer
takes on the shape of the web. A modified web may be used which has
recesses (like the surface of a golf ball) on the same grid as the
contact surface. The resulting sheet will have the space needed for
the elastomer to flow. It may also be possible to form a carrier
sheet which has a recess grid which is much finer than the intended
contact grid. This will eliminate the need to orient the elastomer
relative to the contact array of the device.
Flow space may also be formed by increasing the magnetic field
level during ACE manufacture. This increase in the magnetic force
tends to pull the magnetic particles from the surface and create
columns with an extra particle thickness in the column, but will
leave the rest of the elastomer sheet at its basic thickness. This
extra particle protrudes from the surface of the matrix to form a
convoluted surface (with erupted portions aligned with the
columns), which provides additional space for the elastomer to move
to during compression.
The device of the invention may be used in at least three different
areas in a connector to optimize the interconnection. The device
may be used between two or more components, e.g. a board, to
provide electrical contact. The device may also be used a
component, such as a board, and a heat sink. The latter devices are
preferably highly convoluted to maximize thermal contact. These
convolutions provide the space needed for the material to flow
during compression. The thermal conducting material also generally
comprises a higher percentage of metal particles in the matrix,
preferably between about 20 to 25%, than electrically conducting
material, which preferably comprises less than 12% metal particles.
As a result, the thermal conducting material tends to be more
isotropic than anisotropic. The use of an isotropic thermal
elastomer between the device and heat sink also spreads the
compressive load uniformly across the device, reducing the
opportunity for damage to the device.
Alternatively, the device may be used in addition to a metal
stiffener which is normally required on the back side of the
printed circuit board to maintain a uniform compressive load
between the board and device. An unfilled, insulating elastomer can
be placed between the stiffener and board, to assure a uniform load
across the surface. Although this material behaves like an
incompressible fluid, it will not provide a perfectly uniform load
leveling action. This can be corrected by perforating the elastomer
with an array of holes. This will allow for local deformation,
while assuring a uniform load distribution. Alternatively, the
elastomer may be filled with compressible particles or gas
particles to achieve the same effect. Without perforation of the
elastomer, or creating space by one of the means described above,
true load leveling cannot occur.
In addition to the applications described above, the device may be
used to interconnect device package to device package; board to
board; board to flex or any combination of same.
These elastomeric materials can also be used in the packaging of
the device with one or more components. Rather than use wire
bonding to attach a component to a lead frame package or other
device interconnect structure, a very fine pitch elastomer is used
to attach chip 202 to the lead frame structure (FIG. 17). Device
package 200 comprises chip 202 sandwiched between two layers of
elastomer. A top layer 204 provides thermal contact to remove heat,
via heat sink 208, from the chip, and a bottom layer 206 provides
electrical contact between the chip 202's pad layer and lead frame
210. The combination of elastomers as shown provides excellent
mechanical and environmental protection to the chip. Compression of
the elastomer would occur as can 212 is sealed with swaged seal 214
around base 216.
The device and methods described above primarily used to create a
conducting matrix for subsequent assembly into an interconnection
device. However, other uses are envisioned to integrate the
manufacturing of the conducting matrix directly into the board or
flex circuit manufacturing process. For example, the Mylar carrier
sheet may be replaced by a flex circuit. A sheet of the conducting
matrix would be formed on the surface of the flex circuit and
bonded to it. Interconnection of the flex to the board or device
would be facilitated by compressing the flex circuit/conducting
matrix to the mating contact using appropriate housing and
alignment hardware.
With respect to planarization of BGA devices, the balls of solder
typically have a tolerance on their thickness. The device to which
they are attached may have a certain amount of warpage due to the
construction process and materials used. As a result, the surface
formed by the bottom of the array of solder balls is not a flat
plane, but an irregular shape. The irregular shape constrains the
choice of the interconnection medium because the irregular shape
demands that the interconnection medium have a large dynamic range.
The need for a large dynamic range limits the choices of
interconnection medium and increases the system cost. However, the
device of the invention may be used to make a separable connection
to a BGA by a low cost modification to the package which will
planarize the array, thus allowing the BGA to be readily
connectorized.
Using a heated flat surface which is not wetable by solder, the BGA
package is pressed against the plate. The temperature of the
surface is such that the solder will soften and extrude as the
solder ball is pressed against the surface, with the array of
solder balls conforming to the heated plate. A controlled
compression can be used such that the final dimension from the top
of the package to the plane of the BGA surface is highly
controlled. The resulting array of flattened solder ball surfaces
would now form a true plane. This surface would now be optimized
for interconnection using thin ACE materials. Furthermore, the
bottoms of the balls would each have a flat surface. The balls used
in the BGA package may alternatively comprise a solder-coated metal
ball, rather than a ball consisting entirely of solder. For
purposes of this description, the term "solder ball" refers to both
pure solder balls and solder-coated metal balls.
In a preferred embodiment, the heated flat surface could be a
Teflon coated hot plate with a regulated temperature control. The
final thickness of the device would be controlled by a fixture
attached to the hot plate, with a limiting stop which establishes
the location of the array of flattened solder ball surfaces.
Generally, to carry out the method of the invention, for making an
elastomeric device for electrically interconnecting two or more
components, a plurality of conductive, magnetic particles are
embedded in an elastomer which preferably retains 90% of its
modulus of compression over a temperature range of between about
-50.degree. C. to 200.degree. C. by mixing the particles in the
elastomer before the elastomer sets and applying a magnetic force
to the particles so that the particles align themselves in
electrically isolated columns as the elastomer sets to form an
elastomeric matrix having one or more outer surfaces and comprising
one or more electrically conductive pathways through the matrix.
After the particles are embedded, one or more electrically
conductive contact pads are provided and fixed to the matrix so
that at least a portion of one or more of the pads is flush with or
extends outward from one or more of the outer surfaces of the
matrix and, so that at least a portion of the pad is in at least
intimate contact with one or more of the pathways. The pads may be
fixed to the matrix by sputtering, vapor depositing, plating,
bonding or a combination thereof, with or without the use one or
more carrier sheets and/or support films. Alternatively, the pads
may be fixed to the matrix as an applique of floating or
non-floating pads using the techniques described above.
The device made by the method is enhanced by creating one or more
means for providing flow space into which at least a portion of the
matrix may flow under compression, wherein the step of creating one
or more means for providing flow space comprising one or more of
the following steps: embedding one or more microspheres in the
elastomer as its sets to form the matrix; forming a plurality of
raised surface asperities in one or more of the outer surfaces of
the matrix as the elastomer sets; and/or trapping one or more gas
particles in the matrix as the elastomer sets. The pathways formed
may be anisotropic and comprise up to about 25% magnetic particles
by volume of the elastomeric matrix. The pathways preferably
comprise at least about 3% magnetic particles by volume of the
elastomeric matrix. The method preferably utilizes a plurality of
the columns of magnetic particles wherein at least one end particle
proximate one or more of the outer surface of the matrix, and
wherein one or more of the pads is in intimate contact with an end
particle of one or more of the columns of particles, wherein the
pads preferably comprise one or more layers of metal in at least
intimate contact with one or more of the outer surfaces of the
matrix and one or more of the pathways.
In methods in which an applique of pads are used, the pads are a
known number and comprise two opposing end portions having a
diameter and a middle portion having a diameter smaller than the
diameter of the end portions, and wherein the step of providing one
or more electrically conductive contact pads comprises the steps
of, providing one or more non-conductive, pliant support sheets
comprising a plurality of holes, having a diameter smaller than the
diameter of the end portion of the pads, through the sheet
corresponding to the number of pads; and pushing one of the
opposing ends portions of each of the pads through one of the holes
so that the pad is captured in the sheet.
Although specific features of the invention are shown in some
drawings and not others, this is for convenience only as some
feature may be combined with any or all of the other features in
accordance with the invention. Other embodiments will occur to
those skilled in the art and are within the following claims.
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